This invention relates to a rotating or pivoting apparatus for use in, for example, a copy machine for picking up and transferring a medium such as a copy paper sheet.
There is a medium feeding apparatus for use in, for example, a copy machine, in which sheets of a medium are stacked on a backup plate, and picked up one by one in the order beginning from an uppermost one in accordance with the rotation of a pickup roller incorporated in the apparatus. The backup plate is urged upward by a spring member, thereby pressing the uppermost medium member against the pickup roller. The pickup roller has its surface coated with a rubber member and hence has a frictional force.
Since the sheets of the medium stacked on the backup plate have substantially the same frictional force, it is possible that other sheets placed under the uppermost one in contact therewith will be picked up simultaneously with the uppermost one during the rotation of the pickup roller. To avoid this, a separating mechanism is provided on the medium-picking side of the pickup roller for separating the sheets of the medium from each other. The separating mechanism includes a forwarding roller and an interrupting roller opposed to the forwarding roller. The forwarding roller and the pickup roller are synchronous with each other and rotate in the same direction. The interrupting roller is fixedly opposed to the forwarding roller, with a gap corresponding to one sheet interposed therebetween.
When a plurality of sheets of the medium in a stacked state have been picked up by the pickup roller, only the uppermost one passes through the gap between the forwarding roller and the interrupting roller, while the remaining sheets of the medium are interrupted by the interrupting roller. Further, each sheet of the medium forwarded in accordance with the rotation of the forwarding roller is sensed by a sensor, and the rotation of the pickup roller is stopped depending upon the sensing result. After each sheet of the medium passes the sensor, the sensor determines that each sheet has been sent to a later process, thereby rotating the pickup roller to pick up the next sheet of the medium.
Medium feeding apparatuses constructed as above are widely used for various purposes. Accordingly, these apparatuses treat various types of mediums that have different thicknesses or friction factors, or may be easily worn or deformed.
In light of the above, an apparatus is demanded which can reliably pick up and transfer various types of mediums one by one, and at the same time can execute a high-speed operation or can deal with a great amount of mediums.
However, in the prior art, each medium is pressed with a great force of, for example, about 1-5 N in light of, for example, deformation of each medium. This force is much higher than that necessary for forwarding mediums.
In general, when forwarding stacked sheets of a medium using a frictional force, the greater the force applied to each sheet to press it against the pickup roller, the larger the number of sheets to be forwarded simultaneously. Therefore, it is necessary to minimize the pressing force applied to each sheet. If, however, the pressing force is too small, slippage may occur between each sheet and the pickup roller. To avoid this, the pressing force applied to a medium is set at a high value in the prior art. As a result, it is possible that a plurality of sheets of a medium are simultaneously picked up by the pickup roller, thereby increasing the load on the separating mechanism that separates sheets of a medium from each other. In other words, the separating mechanism may not separate the sheets reliably.
When the pickup roller simultaneously picks up a plurality of sheets of a medium, it is desirable that a dedicated sensor should promptly sense it to thereby stop the rotation of the pickup roller. However, there is no space between the pickup roller and the separating mechanism, and hence such a sensor cannot be provided. This being so, a plurality of sheets of a medium, if simultaneously picked up, cannot promptly be sensed and the pickup roller cannot be stopped.
Since in the prior art, the rotation of the pickup roller is stopped on the basis of a signal output from a sensor provided downstream of the separating mechanism, large portions of sheets of a medium have been forwarded when the rotation of the pickup roller has been stopped.